Liquid phase oxidation of a mixture of alkanes and alkenes with air



Feb. 5, 1957 N. c. ROBERTSON V 2,780,634

LIQUID PHASE OXIDATION OF A MIXTURE or ALKANES AND ALKENES WITH AIR Filed July 13, 1954 2 Sheets-Sheet 1 {Pressure Relief Valve l2 Ven'l' la Cooling I Condenser Neulralizing "l7 Medium J (e.g. dilul 'e aqueous 5 solul'ion of NaHCOg) IO M v} I 7 Organic Solvenl I Reflux (e.g. Benzene) ll r Reacl'or H ea er v Temp Neu'l'ralizing} /I l3o-3ooc v Pressure 300 psig Organic Solvenl' (e.g.Benzene) Propylene L IS M A A Propane 7 ll Reac'lion Produds l A, Unreacl'ed Propylene l Propylene-Propane 0nd p I Mix'l'ure I Anhydrous l Dns'hllahon Organic Solveni 2 Apporifllis Recycle S o l I Reac'l'ion Propylene Producls Oxide Dis+illa+ion 22 scpqrqfion Organic Solvenl S r f I Apparalus propylene eu ra lzlnq Prehea'ler I i M.d'um

' Reac'lion Producls S'lripped of Anhydrous Acids and Wal'er Organic Solvenl' INVENTOR. Recycle & N R! key/I014 FIGLI OM JW ATTORNEX United States Patent" LIQUID PHASE OXIDATION OF A M XTURE F ALKANES AND ALKENES WITH AIR Nat C. Robertson, Wellesley, Mass., assignor, by mesne assignments, to Escambia Chemical- (Zorporation, Pace, Flar, a corporation of Delaware Application July 13, 1954, Serial No. 443,037

4 Claims. (Cl. 260-4485) This invention relates to the production of chemicals and in particular to the production of olefin oxides.

A principal object of the present invention is to produce oxygenated hydrocarbons in good yields by the liquid phase oxidation of unsaturated hydrocarbons in a waterim-miscible organic solvent with an elemental-oxygencontaining gas.

Another object of the present invention is to provide improved processes for the manufacture of olefin oxides from olefins.

Still another object of the present invention is to pro vide a process of the above type which is particularly adapted to the production of oxygenated hydrocarbons containing at least three carbon atoms and in particular propylene oxide.

Other objects of the invention will in part be obvious and will in part appear hereinafter.

'i he invention accordingly comprises the process involving the several steps and the relation and the order of one or more of such steps with respect to each of the others which are exemplified in the following detailed disclosure, and the scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects. of the invention, reference should be had to the following detailed description taken in connection with the accompanying drawings wherein:

Fig. l is a diagrammatic llow sheet illustrating one embodiment of the invention, and

Fig. 2 is a diagrammatic flow sheet illustrating another preferred embodiment of the invention.

In the present invention, an olefin is oxidized to the corresponding olefin oxide accordance with the general procedures described more fully in our copending appli cation Serial 401,347, filed December 30, 1953. A preferred specific embodiment of the present invention utilizes propylene as the olefin to be oxidized and the invention will be initially described in connection with the oxidation of propylene without attempt to limit the scope thereof. This oxidation is preferably achieved by passing an elemental-oxygen-containing gas through a liquid phase containing dissolved propylene. The liquid phase also includes a dissolved saturated hydrocarbon which is preerably propane. The liquid phase is preferably a water-immiscible organic solvent which is relatively inert to oxygen under the reaction conditions, the preferred solvent being benzene. The oxygen-containing gas is preferably air which is introduced into a reactor through an air disperser.

it has been found that mixtures of propylene and pro.- pane fed to the reactor provide higheryields of propylene oxide per gram of propylene fed than are obtained without the addition of the propane, other conditions being the same. it is also highly desirable that the reaction mixture be continuously withdrawn. from the reactor-and extracted at room temperature by a solvent immiscible 2,780,634 aten d Feb- 5 3. 5.7

medium capable of neutralizing organic acids. In a preferred embodiment of the invention, the extraction medium is preferably a dilute aqueous solution of sodium bicarbonate, as described more fully in our copencling application Serial No. 401,347. This continuous extraction has a threefold advantage in that (1) the water formed during the reaction is continuously separated so as to maintain the oxidation zone substantially anhydrous, thus minimizing hydrolysis of the oxide; 2) the acids formed during the oxidation are neutralized, thus also lessening any hydrolysis efiect; and (3) the formation of polymeric materials is minimized.

The invention will be particularly described in connection with the oxidation of propylene to propylene oxide, it being understood that the invention is set forth in the following non-limiting examples, the reference numerals indicating the appropriate sections of the flow sheet illustrated in the drawings.

Exmmple I The solvent, 620 mls. of benzene, along with 1.4 grams of a manganese propionate catalyst, is charged to a high pressure reactor Ill. An extractor 18 is charged with a mixture consisting of 4.58 liters of 0.336 N sodium bicarbonate solution adjusted to a pH 7 with phosphoric acid and 1.77 liters of benzene. The reactor is then put under about 300 p. s. i. of nitrogen and charged with 666 grams of a propylenepropane mixture. The quantity of propylene in the mixture amounted to 333 grams while the remainder of the mixture consists of propane. The reaction mixture is brought up to the operating temperature within the range of C..225 C. by means of a heater schematically indicated at 11. The pressure relief valve 13 is then adjusted to maintain a pressure of about 750 p. s. i. The b enezne-propylene-propane mixture is then recirculated for about one hour so as to distribute. the propylene and propane evenly to the extractor. At

.this point, the nitrogen feed is stopped and a steady rate of air feed, between 4 to 5 standard cubic feet perihour, is, commenced. The withdrawal and recirculation of the reaction mixture from the reactor commenced above is continued. A propylene-propane mixture comprising about 50% by weight propylene and 50% by weight propane is fed to the reactor at a rate of about 1-15 grams per hour so as to make up for the loss of propylene and propane in the purge gas and for that which has reacted. The withdrawn reaction mixture is pumped by means of a pump 14 through a cooler 16 at a rate of approximately 50.00 mls. per hour, wherein it is cooled to room temperature. The cooled reaction mixture is then passed into an extractor 18 and upwardly through the dilute sodium bicarbonate solution, wherein theore ganic acids are neutralized. ture collects in the settling layer :of benzene on top of the dilute sodium bicarbonate solution where entrained. water settles out. The benzene layer is continuously withdrawn and recycled back to the reactor after first being preheated ,to the temperature of the reaction as indicated at 22. The rate of circulation of the reaction mixture is sufficiently high so as to give a complete cycle of the reactor contents through the extractor 18 in about 15 minutes. Condenser 12conti-nuously refiuxes propylene and propane back to the reactor 1-0 so as vto provide for high conversion of the propylene to oxygenated products. During a run of almost 5 hours duration, 574 gra ns ,of the propylene-propane mixture were fed ,to the reactor. After termination of the run, the, products are ;recovered by employing any of the well-known separatign techqu ch s a distil on s iad aa e at 2.0-; The

above'run produced the following, materials, the yields of.

The extracted organic mixwhich are indicated as grams of product per 100 grams of hydrocarbon consumed.

Example I I This reaction was carried out as in Example l (under approximately the same conditions of temperature, pressure, solvent, etc.) except that the reactor was initially charged with 520 grams of a propylene-propane mixture. The quantity of propylene in the mixture amounted to 390 grams while the remainder, 130 grams, consisted of propane. Also 336 grams of the propylene-propane mixture were fed to the reactor during the run of about 5 hours duration. The quantity of propylene in the feed mixture amounted to 252 grams while the remainder, 84 grams, consisted of propane. The propylene-propane mixture in this reaction thus was composed of about 75% by weight propylene and 25% by weight propane. The above run produced the following materials, the yields of which are indicated as grams of product per 100 grams of hydrocarbon consumed.

Grams Propylene oxide 44.75 Propylene glycol 22.10 C1 and C2 acids 16.65 Polymeric material 17.40 Carbon oxides 26.30 Other products 40.90

Example III This reaction was carried out as in Example 1 (under approximately the same conditions of temperature, pressure, catalyst, solvent, etc.) except that the reactor was initially charged with 495 grams of only propylene. Also 430 grams of only propylene were fed to the reactor during the run of almost 5 hours duration. The above run produced the following materials, the yields of which are indicated as grams of product per 100 grams of propylene consumed.

Grams Propylene oxide 29.8 Propylene glycol 30.3 C1 to C4 acids 19.9 Polymeric materials 27.7 Carbon oxides 33.6 Light boiling products 20.8 Other products 12.7

One preferred method of operating the process on a continuous basis is illustrated in Fig. 1, wherein the condenser 12 continuously refiuxes propylene, propane and other products which are recycled back to the bottom of the reactor. Some of the reaction mixture in the reactor 10 is continuously withdrawn and pumped through a cooler 16 wherein it is cooled to room temperature. The cooled reaction mixture is then passed upwardly through an extractor containing a lower layer of a neutralizing medium and an upper layer of the same water immiscible organic solvent as used in the reactor. The neutralizing medium is preferably a solvent-immiscible solution capable of neutralizing organic acids. This continuous countercurrent extraction step thus provides for the continuous removable of water and neutralization of organic acids. The portion of the lower layer which is continuously being withdrawn is fed to a distillation apparatus 19 wherein the neutralizing medium is stripped of any dissolved propylene oxide. A fresh supply of a neutralizing medium (e. g., dilute aqueous solution of sodium bicarbonate) from a suitable storage 17 is fed to the extractor 18 so as to maintain the level and pH of 4 the lower layer constant. The extracted reaction mixture which has collected in the upper organic solvent settling layer is then withdrawn from the extractor 18 and fed to the distillation separation apparatus 20 (which may include several conventional stills) so as to provide for the separation of the reaction products and removal of any small quantities of water that may be present. The unreacted propylene and propane is recycled back to the reactor 10. The substantially anhydrous organic solvent is also recycled back to the reactor 10 after first being preheated, as indicated at 22, to the temperature of the reaction.

Another preferred method of operating the process on a continuous basis is illustrated in Fig. 2, wherein the condenser 12 continuously refiuxes propylene, propane and other products which are recycled back to the bottom of the reactor 10. Some of the reaction mixture in the reactor 10 is continuously withdrawn and passed into a distillation apparatus 15 wherein propylene oxide, propylene and propane are distilled 011. The unreacted propylene and propane are then recycled back to the reactor 10. The propylene oxide-free reaction mixture may then be cooled, neutralized and dehydrated in the same manner as described in the discussion of Fig. 1. Other alternative methods of treatment of the propylene oxidefree reaction mixture are possible, however. For example, the cooling step may be eliminated and the propylene oxide-free reaction mixture may be neutralized and extracted while hot. Water may be removed from the hot reaction mixture either by interposing a suitable dehydrator before or after the extractor 18 or by interposing a suitable azeotropic distillation apparatus such as is indicated by the dotted lines at 21. The removal of water may also be provided for at the distillation separation apparatus 20. The process can also be operated on a continuous basis such that the reaction mixture is cooled, neutralized and dehydrated prior to stripping out the propylene oxide. By continuously removing propylene oxide from the reaction mixture as soon as possible after the mixture is withdrawn from the reactor, a substantially higher ratio of propylene oxide to propylene glycol is obtained than would be if the propylene oxide were not removed.

In connection with the above preferred continuous methods, it is also feasible to subject the reflux from the condenser 12 to continuous distillation and/or extracting steps so as to remove any oxide contained therein and thus obtain maximum oxide recovery, as shown in dotted lines in Fig. 2.

While specific examples of the present invention have been given above, they are subject to wide variations without departing from the scope thereof. For example, the manganese propionate (of about 0.1% concentration) is a well-known oxidation catalyst. Other manganese salts or salts or oxides of other metals of variable valence are equally effective. An important purpose of utilizing an oxidation catalyst is to prevent the possible accumulation of large concentrations of dangerously explosive hydroperoxides. It is believed that the metal walls of the reaction chamber may have sufiicient catalytic effect to prevent the accumulation of appreciable amounts of hydroperoxides.

The hydrocarbon feed stream preferably comprises a mixture of an olefin and a saturated hydrocarbon. In one preferred embodiment of the invention, the feed stream preferably comprises a mixture of propylene and propane. The quantity of propylene in the feed mixture is maintained sufficiently high so that the weight percent of propylene present during the oxidation is on the order of above about 5% of the solvent and preferably on the order of about 20% of the solvent. The presence of appreciable quantities of propane in the feed stream has been found to have a most beneficial etfect in that it aids in minimizing the formation of polymeric materials and thus makes it possible to obtain higher propylene oxide yields. This beneficial effect is well illustrated in a comparison of Examples I and II, which employ a mixed propane-propylene feed, with Example III, which employs a straight propylene feed. In Examples I and II, it can be seen that higher yields of propylene oxide and lower yields of polymeric materials were obtained per gram of hydrocarbon consumed than were obtained in Example III.

The specific procedure described for the oxidation of propylene in a propylene-propane mixture can be applied to other olefin-saturated hydrocarbon mixtures. For examle, the olefin contained in a mixture comprised of an olefin containing from about 4 to about 8 carbon atoms and the corresponding saturated hydrocarbon can also be oxidized to its oxide according to the procedure of the present invention. Additionally, it is also possible to employ a mixture of an olefin and a dissimilar saturated hydrocarbon, for example, propylene-butane.

The continuous extracting step serves several advantageous functions. First, the organic acids formed during the oxidation are neutralized by the neutralizing medium.

This serves to lessen any hydrolysis effect on the oxide that would occur under acidic conditions. Secondly, as a consequence of removing organic acids from the oxidation zone, the formation of polymeric materials is minimized and thus higher oxide yields are obtainable. Thirdly, the water formed during the reaction is continuously removed so as to maintain the oxidation zone substantially anhydrous. By maintaining the hot oxidation zone which contains acidic materials substantially anhydrous, hydrolysis of the oxide is again minimized.

The neutralizing medium in the extractor is preferably a solvent-immiscible solution capable of neutralizing organic acids. While a dilute aqueous sodium bicarbonate solution has been illustrated as the preferred neutralizing medium, other aqueous solutions such as dilute sodium hydroxide, sodium carbonate, etc. may be employed. Polar organic materials or their Water solutions capable of removing organic acids may also be employed as suitable neutralizing media. Likewise, a straight, highly etiicient water extraction may also be employed to remove the water-soluble organic acids.

When the reaction mixture to be extracted still contains the oxide, it is preferable to neutralize and extract the mixture with a dilute aqueous medium such as illustrated in Example I. The medium in this case is maintained neutral, i. e., adjusted to a pH 7, so as to prevent hydrolysis of the oxide which would occur if the medium became too basic or acidic. When the reaction mixture to be neutralized and extracted has been stripped of all oxide, then it is possible to employ a somewhat more basic medium in the extractor.

The range of operating pressures and operating temperatures is quite broad and can be varied within considerable limits. With regard to pressure, it should be pointed out that it is preferably maintained above 300 pounds per square inch but that considerably higher pressures may be utilized where design considerations indicate the desirability of such higher pressures. The temperature Within the reactor may be varied between about 130 C. and 300 C., the temperature remaining below the critical temperature of the organic solvent in all cases.

While benzene has been illustrated as being a preferred water-immiscible organic solvent in the oxidation of propylene contained in a propylene-propane mixture, other relatively inert water-immiscible organic solvents can be used, e. g., tertiary butyl benzene. The preferred organic solvents are those which are inert to oxygen and the olefin oxide, which will dissolve large concentrations of the olefin, and are substantially water immiscible to restrict the quantity of water present in the oxidation zone. Thus the water-immiscible organic solvent admits very little, or minute, quantities of water into the oxidation zone at any one time so that hydrolysis of the formed oxide to the corresponding glycol is minimized at reaction conditions. In Example I there is illustrated a recycle time of approximately 15 minutes for passing all of the reactor contents through the extractor. This may be considerably shorter wherethe heat balance condi tions permit of economical operation with higher recycle rate. Equally, it can be somewhat longer, although best results are obtained when the cycle time is very short.

Since certain changes may be made in the above process without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. In the method of producing an olefin oxide by dis solving a monoolefin containing from three to eight carbon atoms in a water-immiscible liquid hydrocarbon solvent which is inert to oxygen, passing an elementaloxygen-containing gas into the solution while the solution is held under pressure and maintained at a temperature above about C., maintaining in the solution a low concentration of at least one compound selected from the group consisting of water, organic acids and olefin oxide, and recovering olefin oxide, the improvement which comprises dissolving with said monoolefin in the solvent a saturated hydrocarbon containing from three to eight carbon atoms.

2. In the method of producing an olefin oxide by dissolving a monoolefin containing from three to eight carbon atoms in a water-immiscible liquid hydrocarbon solvent which is inert to oxygen, the weight percent of the monoolefin being continuously maintained on the order of above about 5 percent of the solvent during the oxidation, passing an elemental-oxygen-containing gas into the solution while the solution is held under pressure and maintained at a temperature above about 130 0., maintaining in the solution a low concentration of at least one compound selected from the group consisting of water, organic acids and olefin oxide, and recovering olefin oxide, the improvement which comprises dissolving with said monoolefin in the solvent a saturated hydrocarbon containing from three to eight carbon atoms.

3. In the method of producing propylene oxide by dissolving propylene in a water-immiscible liquid hydrocarbon solvent which is inert to oxygen, passing an elementaloxygen-containing gas into the solution While the solution is held under pressure and maintained at a temperature above about 130 C., maintaining in the solution a low concentration of at least one compound selected from the group consisting of water, organic acids and propylene oxide, and recovering propylene oxide, the improvement which comprises dissolving propane in the solvent with said propylene. 4. In the method of producing propylene oxide by dissolving propylene in benzene solvent, the weight percent of said propylene being continuously maintained on the order of above about 5 percent of the benzene solvent during the oxidation, passing an elemental-oxygen-containing gas into the solution while the solution is held under pressure and maintained at a temperature above about 130 C., maintaining in the solution a low concentration of at least one compound selected from the group consisting of water, organic acids and propylene oxide and recovering propylene oxide, the improvement which comprises dissolving propane in the solvent with said propylene.

References Cited in the file of this patent UNITED STATES PATENTS 2,316,604 Loder Apr. 13, 1943 2,366,724 Gardner Ian. 9, 1945 2,475,605 Prutton et al July 12, 1949 2,530,509 Cook Nov. 21, 1950 2,644,837 Schweitzer July 7, 1953 2,689,253 Robertson et al. Sept. 14, 1954 

1. IN THE METHOD OF PRODUCING AN OLEFIN OXIDE BY DISSOLVING A MONOOLEFIN CONTAINING FROM THREE TO EIGHT CARBON ATOMS IN A WATER-IMMISCIBLE LIQUID HYDROCARBON SOLVENT WHICH IS INERT T OXYGEN, PASSING AN ELEMENTALOXYGEN-CONTAINING GAS INTO THE SOLUTION WHILE THE SOLUTION IS HELD UNDER PRESSURE AND MAINTAINED AT A TEMPERATURE ABOVE ABOUT 130*C., MAINTAINING IN THE SOLUTION A LOW CONCENTRATION OF AT LEAST ONE COMPOUND SELECTED FROM THE 